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Unformatted text preview: Zachary Bergman Cell Bio 318 2/7/10 Assignment #4 1) Why do you think the authors tested both WT LKB1 and GFP tagged LKB1 in their assays? What did they use as a negative control? In previous studies the LKB1 protein exhibited weak catalytic activity in both in vivo and in vitro experiments so it is possible that addition of the GFP tag could dampen its activity further and this would prevent the success of these experiments. Fortunately for the authors the GFP protein still functioned and was exported from the nucleus after phosphorylation in the presence of the wildtype so this problem did not affect the experiment. As the negative control they used the LS174T-S2 cell line in which, even in the presence of STRAD, LKB1 is not phosphorylated and thus stays in the nucleus. 2) The authors start with the observation that both STRAD and LKB1 are reduced in intestinal epithelial cancer lines. What experimental evidence do they provide to demonstrate that both STRAD and LKB1 are in fact required for polarization of the LS174T and DLD-1 cells?...
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